Abstract: Acoustic frictional resistance comprises a plate having at least one laser-formed hole therethrough. The plate is formed by positioning a plate preferably one having a thickness smaller than one and one-half milimeters alongside a laser and directing the laser beam so that it cuts a hole through the plate. During the process of producing the resistance, the value of the acoustic friction is measured as a pressure drop of a constant air stream or as an expenditure of electrical energy for an electrically excited electroacoustic transducer. This measurement is then used as a variable or as a standard for controlling the process. Advantageously, a coherent beam is emitted by the laser which is deflected by mirror from a horizontal to a vertical direction and focused by means of a lens to work in a contact-free manner on a workpiece supported on a support member such as a movable table. By moving the table in two coordinate directions, a plurality of bores are formed in a pattern in a workpiece.

Abstract: A circuit in an electroacoustic transmission system suppresses amplitude peaks which are caused by the utterance of a stop consonant such as a "P". A microphone of the transmission system has an output which a high-pass filter is connected. The high-pass filter is normally inactive but can be activated by an electronic switch for a brief period of time. The switch is controlled by a train of electronic elements functioning as a detector for detecting a characteristic quiescent or pause period before the explosive discharge of the stop consonant. Upon detecting this pause the electronic switch is activated and held activated for about 10 to 30 ms. During that time the peak occurs but is suppressed in that it is not passed by the high-pass filter which is activated during this time.